The proliferation of portable electronic devices such as cell phones and laptop computers has lead to an increased demand for high capacity, long endurance light weight batteries. Because of this alkali metal batteries, especially lithium ion batteries, have become a useful and desirable energy source. Lithium metal, sodium metal, and magnesium metal batteries are well known and desirable energy sources.
By way of example and generally speaking, lithium batteries are prepared from one or more lithium electrochemical cells containing electrochemically active (electroactive) materials. Such cells typically include, at least, a negative electrode, a positive electrode, and an electrolyte for facilitating movement of ionic charge carriers between the negative and positive electrode. As the cell is charged, lithium ions are transferred from the positive electrode to the electrolyte and, concurrently from the electrolyte to the negative electrode. During discharge, the lithium ions are transferred from the negative electrode to the electrolyte and, concurrently from the electrolyte back to the positive electrode. Thus with each charge/discharge cycle the lithium ions are transported between the electrodes. Such rechargeable batteries are called rechargeable lithium ion batteries or rocking chair batteries.
The electrodes of such batteries generally include an electrochemically active material having a crystal lattice structure or framework from which ions, such as lithium ions, can be extracted and subsequently reinserted and/or permit ions such as lithium ions to be inserted or intercalated and subsequently extracted. Recently, a class of transition metal phosphates and mixed metal phosphates have been developed, which have such a crystal lattice structure. These transition metal phosphates are insertion based compounds like their oxide based counterparts. The transition metal phosphates and mixed metal phosphates allow great flexibility in the design of lithium ion batteries.
Recently, three-dimensional structured compounds comprising polyanions such as (SO4)n−, (PO4)n−, (AsO4)n−, and the like, have been proposed as viable alternatives to oxide based electrode materials such as LiMxOy. A class of such materials is disclosed in U.S. Pat. No. 6,528,003 B1 (Barker et al.) The compounds therein are of the general formula LiaMIbMIIc(PO4)d wherein MI and MII are the same or different. MI is a metal selected from the group consisting of Fe, Co, Ni, Mn, Cu, V, Sn, Ti, Cr and mixtures thereof. MII is optionally present, but when present is selected from the group consisting of Mg, Ca, Zn, Sr, Pb, Cd, Sn, Ba, Be, and mixtures thereof. More specific examples of such polyanion based materials include the olivine compounds such as LiMPO4, wherein M=Mn, Fe, Co and the like. Other examples of such polyanion based materials include the NASICON compounds such as Li3M2(PO4)3, and the like.
Although these compounds find use as electrochemically active materials useful for producing electrodes these materials are not always economical to produce, they may afford insufficient voltage, have insufficient charge capacity or exhibit low ionic conductivity. The present invention provides an economical, reproducible and efficient method for producing metal phosphates and mixed metal phosphates with good electrochemical properties which make them useful for producing electrodes and in particular cathodes.